Caffeine is a colourless material that occurs naturally in the tea plant. The wide-spreading myths that darker colour teas have more caffeine, or the less oxidation the leaves the less caffeine are all sheer myths.
While it is true that various manners of processing do have effects on the final quantity of caffeine content, the quality of the plucks (ie the green leaves before processing) as a result of the specific tea cultivar, phrase of leaf development, pluck position, horticultural conditions, the season and the very weather during the picking have a more profound influence (1, 2). This applies to caffeine, as it does to any other tea substances.
The College of Medicine of National Taiwan University did a study (1) in cooperation with the Taiwan Tea Experiment Station in Taipei to find out in details from a range of 31 tea selections what exactly the differences are. Some of these selections are the same variety on purpose. Their research covered a few things, but let’s look at the results about caffeine. The scientists have based their data on steeping the tealeaves in 100°C water for 30 minutes, so it is likely that you get less caffeine even if you are buying the very same batch of tea when you infuse it normally for drinking.
To supplement their findings for the purpose of a general idea for making decisions in real life purchase, we have also integrated the findings of another study in Beijing (3) involving 39 tea selections and another one in Massachusetts (4).
A few things jump out as obvious in the chart:
- The same variety of tea can have different levels of caffeine. For example, a sencha can have either 26mg/g or almost 32mg/g.
- The green tea samples generally has more caffeine than other groups in the selections
- The amount of caffeine in the green tea group vary not so much according to leaf size, but likely to region, cultivar, or other horticultural difference (5). For example, the larger leaf green tea Long’jing, which is from Taiwan, has more caffeine than the two smaller leaf samples from Zhejiang. Leaf size differences in normal leaf tea green tea production is not as huge as between tea categories. For example, the production of a number of traditional oolong, particularly Wuyi and Phoenix, normally employs much larger leaves than most green or black teas.
- With the exception of the two new cultivar Red Cloak (Xiao Hong’pao, as different from Da Hong’pao) selections, the two oolong groups generally have lesser caffeine than other groups
- The one sample of new tea Tieguanyin (6) has the lowest caffeine content amongst all the samples.
- The Taiwan oolong can have 40% less caffeine upon 4 years of maturing when compared to its newer counterparts
- A 20-year-old pu’er has more caffeine than a newer one and far more than a 4-year-old oolong
- Grounded oolong tea and the Lipton teabag, even though they are of lesser quality, they still have very high caffeine contents relative to others in the group
Again, it is important to know that the samples above illustrate only a tiny fraction of tea varieties and they are not comprehensive enough to reflect any general principle for generalization. They are however, good to demystify many wrong perceptions. It’s also good to know that there is an example of oolong that matures to lesser caffeine, because we all love matured oolongs here.
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